Secondary batteries which are highly applicable to various products and exhibit superior electrical properties such as high energy density, etc. are commonly used not only in portable devices but also in electric vehicles (EVs) or hybrid electric vehicles (HEVs) driven by electrical power sources. The secondary battery is drawing attentions as a new energy source for enhancing environment friendliness and energy efficiency in that the use of fossil fuels can be reduced greatly and no byproduct is generated during energy consumption.
Secondary batteries widely used at the preset include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries and the like. An operating voltage of the unit secondary battery cell, namely a unit battery cell, is about 2.5V to 4.6V. Therefore, if a higher output voltage is required, a plurality of battery cells may be connected in series to configure a battery pack. In addition, depending on the charge/discharge capacity required for the battery pack, a plurality of battery cells may be connected in parallel to configure a battery pack. Thus, the number of battery cells included in the battery pack may be variously set according to the required output voltage or the demanded charge/discharge capacity.
Meanwhile, when a plurality of battery cells are connected in series or in parallel to configure a battery pack, it is common to configure a battery module composed of at least one battery cell first, and then configure a battery pack by using at least one battery module and adding other components. Here, the battery cells configuring the battery module or the battery pack are generally pouch-type secondary batteries that may be easily stacked on one another.
In the conventional battery module, the battery cell may be ignited inside the case due to overcharging or the like. When the ignition occurs, if a flame generated from the battery cell is exposed to the outside of the case, it may lead to a larger secondary damage. Meanwhile, if the gas generated during ignition does not escape from the case, the pressure inside the case may rise, which may lead to explosion of the battery module.
Thus, when the battery cell is ignited due to overcharging, it is demanded to find a way to prevent the flame from being exposed to the outside of the case and also to easily discharge the gas out of the case.